Groundwater salinity is a major issue across the world due to its adverse impacts on environment and agricultural productivity. Several types and amounts of salts from diverse sources can be dissolved into groundwater system, as this water system interacts with different processes along its flow direction. Understanding the hydrogeochemical processes or sources of dissolved salts in groundwater is vital for an effective salinity management plan. In this study, the groundwater hydrochemistry of Muttama catchment (1059km2), in southern NSW, Australia, is used to investigate the nature and origin of solutes, causing groundwater salinity. Major ion chemistry together with physicochemical parameters of groundwater were measured at mostly two month intervals over a two and half year period (December 2013 to February 2016) from twenty two piezometers across the catchment.
Most of the groundwaters in the Muttama catchment are Na-Cl dominant except for a few, which are Ca-Cl type water. At low salinity locations weathering of aquifer substrates (up to 53% of total dissolved solids) influences the composition of the groundwater. However, cyclic or evaporated salts with minor weathering inputs are most likely the primary source of solute in the high saline groundwater. Furthermore, evapotranspiration processes could concentrate the salt concentration in some shallow groundwater systems, particularly on the western side of the catchment. The hydrochemistry in this catchment is more variable in space than in time, suggesting that aquifer substrate is a major determinant of the salinity. The outcome of this study will assist to improve the current management strategy in order to mitigate groundwater salinity in the Muttama Catchment.
Key Words: Groundwater salinity, hydrochemistry, weathering, evapotranspiration